EXTRA days charged by AROUNDABOUTCARS and subtracted from deposit without informing client

This company acts as a middle man for car rentals When I got the refund of my deposit they charged a huge amount extra Car was returned on time, no damages When I contacted the rental company it transpired that Aroundaboutcars booked the car for 2 days less and expected me to pay for extra 2 days!-when I contacted AROUNDABOUTCARS they said it could have been a "system error' ????? I PHONED TO SPEAK TO THE MANAGER/PERSON IN CHARGE and still waiting for a reply I asked for a new correct invoice and have not received it Shocking !! I will NEVER use them again!